[RFC 1/2] drm/dsi: Create dummy DSI devices

[Archit Taneja]

We can have devices where the data bus is MIPI DSI, but the control bus
is something else (i2c, spi etc). A typical example is i2c controlled
encoder bridge chips.

Such devices too require passing DSI specific parameters (number of data
lanes, DSI mode flags, color format etc) to their DSI host. For a device
that isn't 'mipi_dsi_device', there is no way of passing such parameters.

Provide the option of creating a dummy DSI device. The main purpose of
this would be to attach to a DSI host by calling mipi_dsi_attach, and
pass DSI params.

Create mipi_dsi_new_dummy for creating a dummy dsi device. The driver
calling this needs to be aware of the mipi_dsi_host it wants to attach
to, and also the DSI virtual channel the DSI device intends to use.

Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_mipi_dsi.c | 78 ++++++++++++++++++++++++++++++++++++++++--
 include/drm/drm_mipi_dsi.h     |  2 ++
 2 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index 2d5ca8ee..9bfe215 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -47,7 +47,14 @@
 
 static int mipi_dsi_device_match(struct device *dev, struct device_driver *drv)
 {
-	return of_driver_match_device(dev, drv);
+	if (of_driver_match_device(dev, drv))
+		return 1;
+
+	if (!strcmp(drv->name, "mipi_dsi_dummy") &&
+			strstr(dev_name(dev), "dummy_dev"))
+		return 1;
+
+	return 0;
 }
 
 static const struct dev_pm_ops mipi_dsi_device_pm_ops = {
@@ -171,6 +178,67 @@ of_mipi_dsi_device_add(struct mipi_dsi_host *host, struct device_node *node)
 	return dsi;
 }
 
+static int dummy_probe(struct mipi_dsi_device *dsi)
+{
+	return 0;
+}
+
+static int dummy_remove(struct mipi_dsi_device *dsi)
+{
+	return 0;
+}
+
+static void dummy_shutdown(struct mipi_dsi_device *dsi)
+{
+}
+
+static struct mipi_dsi_driver dummy_dsi_driver = {
+	.probe = dummy_probe,
+	.remove = dummy_remove,
+	.shutdown = dummy_shutdown,
+	.driver.name = "mipi_dsi_dummy",
+};
+
+static int mipi_dsi_device_add_dummy(struct mipi_dsi_device *dsi)
+{
+	struct mipi_dsi_host *host = dsi->host;
+
+	dev_set_name(&dsi->dev, "%s.dummy_dev.%d", dev_name(host->dev),
+			dsi->channel);
+
+	return device_add(&dsi->dev);
+}
+
+struct mipi_dsi_device *mipi_dsi_new_dummy(struct mipi_dsi_host *host, u32 reg)
+{
+	struct mipi_dsi_device *dsi;
+	struct device *dev = host->dev;
+	int ret;
+
+	if (reg > 3) {
+		dev_err(dev, "invalid reg property %u\n", reg);
+		return ERR_PTR(-EINVAL);
+	}
+
+	dsi = mipi_dsi_device_alloc(host);
+	if (IS_ERR(dsi)) {
+		dev_err(dev, "failed to allocate dummy DSI device %ld\n",
+			PTR_ERR(dsi));
+		return dsi;
+	}
+
+	dsi->channel = reg;
+
+	ret = mipi_dsi_device_add_dummy(dsi);
+	if (ret) {
+		dev_err(dev, "failed to add dummy DSI device %d\n", ret);
+		kfree(dsi);
+		return ERR_PTR(ret);
+	}
+
+	return dsi;
+}
+
 int mipi_dsi_host_register(struct mipi_dsi_host *host)
 {
 	struct device_node *node;
@@ -924,7 +992,13 @@ EXPORT_SYMBOL(mipi_dsi_driver_unregister);
 
 static int __init mipi_dsi_bus_init(void)
 {
-	return bus_register(&mipi_dsi_bus_type);
+	int ret;
+
+	ret = bus_register(&mipi_dsi_bus_type);
+	if (ret < 0)
+		return ret;
+
+	return mipi_dsi_driver_register(&dummy_dsi_driver);
 }
 postcore_initcall(mipi_dsi_bus_init);
 
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index f1d8d0d..d06ba99 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -174,6 +174,8 @@ ssize_t mipi_dsi_generic_write(struct mipi_dsi_device *dsi, const void *payload,
 ssize_t mipi_dsi_generic_read(struct mipi_dsi_device *dsi, const void *params,
 			      size_t num_params, void *data, size_t size);
 
+struct mipi_dsi_device *mipi_dsi_new_dummy(struct mipi_dsi_host *host, u32 reg);
+
 /**
  * enum mipi_dsi_dcs_tear_mode - Tearing Effect Output Line mode
  * @MIPI_DSI_DCS_TEAR_MODE_VBLANK: the TE output line consists of V-Blanking
-- 
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